As is known in the art, rapid thermal anneal (RTA) apparatus has been used in the semiconductor industry for many years. Early, the apparatus was used in processing silicon wafers during an implantation activation phase of the fabrication. One such arrangement uses apparatus wherein a silicon wafer is positioned between a set of horizontally disposed upper heating lamps and a set of horizontally disposed lower heating lamps.
In more recent times, RTA apparatus has been used to alloy metals such as when forming ohmic contacts to the active devices, for example, source and drain contacts for Field Effect Transistors (FETs) formed on compound semiconductor materials, such as GaN or GaAs. In some applications, a susceptor, such as a graphite susceptor, absorbs heat received by radiation from the upper and lower sets of halogen heating lamps. The susceptor absorbs the radiation then transfers its heat to the wafer enclosed within the susceptor by both conduction and re-radiation to heat the wafer and thereby alloy the metals with the semiconductor material and produce the ohmic contacts.
As is also known in the art, various techniques have been used to create a more uniform heating of a silicon wafer with a planar silicon based process such as Bulk CMOS, SOI processes to produce digital/RF type circuitry, see for example: “Temperature non-uniformities during rapid thermal processing of patterned wafers” by Peter Vandenabeele and Karen Maex, Interunmiversity Micro-electronic Center (IMEC) Kapeldreef 75, 3030 Leuven, Belgium; “Thermal Performance Challenges for Rapid Thermal Processing”, by Jeff Hebb, Axcelis Techmologies, Inc. Beverly, Mass., Ilth IEEE International Conference on Advanced Processing of Semiconductors-RTP2003; “Origin of Local Temperature Variation During Spike Anneal and Millisecond Anneal” by R. Beneyton, A. Colin, H. Bono, F. Cacho, M. Didaud, B. Dumont, P. Morin, K. Barla, 16th IEEE International Conference on Advanced Thermal Processing of Semiconductore-RTP2008; and “Pattern effects in Thermal Processing”, by P. J. Timans and Y. Lee, Mattson Technology. For example, one technique used is to provide RTA uniform compensation elements, such as arrays of physically spaced “dummy” fill elements; stand-alone heat absorbing pads or elements used to absorb some of the heat and thereby provide a greater heating uniformity across the wafer.